This week India celebrated a milestone many thought would never come. For the first time in its history an entire year passed without a single case of paralytic polio. The last Indian child to be paralyzed by the virus was an 18 month-old girl diagnosed on January 13, 2011. The end of polio in India had been predicted: there were 790 cases in 2009 and only 42 in 2010. Fingers will remain crossed for the near future–the World Health Organization won’t certify a country as polio-free for three years, since asymptomatic polio can circulate for some time.

The Indian government has spent $2 billion dollars fighting polio–hundreds of millions of polio vaccine doses have been administered in recent years–and it knows it will spend many more millions to keep the infection away. Polio is transmitted via sewage-contaminated drinking water, and that’s unfortunately fairly common in that part of the world. More worrisome is the proximity of Pakistan, India’s next-door neighbor, which had nearly 200 cases of polio last year. Viruses don’t respect international borders–the risk of polio resurfacing in India is substantial.